ACID (Database Properties)

ACID stands for Atomicity, Consistency, Isolation, and Durability, the four properties that make a database transaction reliable. Together they ensure that related changes succeed or fail as a unit and that committed data survives failures.

Why it matters

ACID is why you can transfer money between two accounts without the risk of one side changing and the other not. Relational databases are built around it, while some NoSQL systems relax parts of it for scale. Knowing which guarantees you actually have is essential when designing anything involving payments, inventory, or bookings.

Example

Atomicity   : debit and credit both apply, or neither does
Consistency : constraints (e.g. balance >= 0) hold after commit
Isolation   : concurrent transactions do not see half-done work
Durability  : once committed, data survives a crash

Common mistakes

• Assuming isolation means full serialization. Most databases default to weaker levels, such as read committed.
• Believing consistency in ACID is the same as consistency in the CAP theorem. They are different ideas.
• Assuming every NoSQL database lacks ACID. Several support multi-document transactions.

Related

• Database transaction
• CAP theorem
• Eventual consistency
• Deadlock

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